1. Field of the Invention
The present invention relates to a power generation system, and more particularly, to a power generation system which can prevent an unnecessary operation due to an accident of external grounding.
2. Description of the Related Art
A description will now be provided of a solar power generation system connected to an ordinary low-voltage distribution system with reference to FIG. 9. FIG. 9 is a schematic diagram illustrating conventional connection between a solar power generation system and a low-voltage distribution system. In FIG. 9, A represents a consumer having a solar power generation system, which includes a solar-cell array 1, a system interconnection inverter 2, and a receiving-end earth leakage breaker 3. The solar-cell array 1, serving as a DC power supply, includes solar-cell modules interconnected in series and/or in parallel so as to provide desired voltage and current. The solar-cell array 1 is connected to the system interconnection inverter 2, which is connected to a low-voltage distribution system 4 via the receiving-end earth leakage breaker 3. A load 5 is connected between the system interconnection inverter 2 and the receiving-end earth leakage breaker 3. DC electric power from the solar-cell array 1 is input to the system interconnection inverter 2 in order to be converted into an AC electric power, which is output to the load 5 or the low-voltage distribution system 4. Wiring within the consumer A is provided from the receiving-end earth leakage breaker 3 to the system interconnection inverter 2 and to the load 5. The receiving-end earth leakage breaker 3 detects an accident of grounding by detecting a ground current, and disconnects connection between the inside and the outside of the consumer A so that the accident of grounding does not influence the low-voltage distribution system 4 at the outside of the consumer A.
Other consumers B1 and B2 which do not have power generation facilities are connected to the low-voltage distribution system 4 via respective receiving-end earth leakage breakers 3.
Since the solar-cell array 1 has a large area, an earth floating capacitance 6 is present. Recently, solar-cell modules integrated with a building material, or thin solar-cell modules have been developed as solar-cell modules constituting the solar-cell array 1. Sometimes, a conductive member (a metal plate or the like) is used as a reinforcing material or a substrate material for such a solar-cell module. In such a case, a solar-cell array sometimes faces a metal plate with a short distance and a large area, thereby increasing the earth floating capacitance 6. Particularly when the metal plate is grounded, the solar-cell array has a stable earth floating capacitance. Furthermore, if, for example, water from rain adheres to the surface of the solar-cell array, the earth floating capacitance 6 is sometimes generated via the water.
In accordance with recent tendency toward a higher efficiency, a smaller size, a lighter weight and a lower cost and the like, the system interconnection inverter 2 mostly adopts a transformerless system in which an insulating transformer is not provided.
We found that, if an accident of grounding occurs at another consumer B1 or B2 when the earth floating capacitance 6 is large and the system interconnection inverter 2 adopts the transformerless system, a ground current Ig2 penetrates into the system via the earth floating capacitance 6 of the solar-cell array 1, passes through the system interconnection inverter 2, and is detected by the reception-end earth leakage breaker 3, thereby causing an unnecessary operation. If such an unnecessary operation is generated, the inside of the consumer A having the solar power generation system is disconnected from the low-voltage distribution system 4 and power supply to the inside of the consumer A is failed, although no accident occurs within the consumer A.
The above-described problems are not limited to the solar power generation system. For example, in a wind power generation system or in a power generation system using fuel cells or the like, the same problems also arise if the earth floating capacitance is large. Hence, there is the possibility that the reception-end earth leakage breaker unnecessarily operates due to an accident of external grounding and electric power supply fails within a consumer.
It is an object of the present invention to solve the above-described problems.
It is another object of the present invention to provide a power generation system which can prevent an unnecessary operation of a receiving-end earth leakage breaker due to an accident of external grounding.
According to one aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system to which a plurality of consumers, each having an earth leakage breaker, are connected and one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. An operational time limit of the receiving-end earth leakage breaker of the power generation system is set to a value larger than an operational time limit of the earth leakage breakers provided in the consumers.
According to another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The system also includes ground-direction determination means for determining whether a grounded position is inside or outside the power generation system.
According to still another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The receiving-end earth leakage breaker includes voltage-to-ground detection means, a zero-phase current transformer, zero-phase-current detection means connected to the zero-phase current transformer, phase comparison means connected to the voltage-to-ground detection means and the zero-phase-current detection means, a time-limit selector, connected to the phase comparison means, for selecting a different time limit in accordance with a signal output from the phase comparison means, zero-phase-current-level determination means connected to the zero-phase-current detection means, and contact driving means, connected to the zero-phase-current-level determination means and the time-limit selector, for driving a contact in accordance with an output of each of the zero-phase-current-level determination means and the time-limit selector.
According to yet another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The receiving-end earth leakage breaker includes voltage-to-ground detection means, voltage-to-ground-level determination means connected to the voltage-to-ground detection means, a zero-phase current transformer, zero-phase-current detection means connected to the zero-phase current transformer, zero-phase-current level determination means connected to the zero-phase-current detection means, and contact driving means, connected to the zero-phase-current-level determination means and the voltage-to-ground-level determination means, for driving a contact in accordance with an output of each of the zero-phase-current-level determination means and the voltage-to-ground-level determination means.
According to yet another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The receiving-end earth leakage breaker includes voltage-to-ground detection means, voltage-to-ground-level determination means connected to the voltage-to-ground detection means, a time-limit selector, connected to the voltage-to-ground-level determination means, for selecting a time limit in accordance with an output of the voltage-to-ground detection means, a zero-phase current transformer, zero-phase-current detection means connected to the zero-phase current transformer, zero-phase-current-level determination means connected to the zero-phase-current detection means, and contact driving means, connected to the zero-phase-current-level determination means and the time-limit selector, for driving a contact in accordance with an output of each of the zero-phase-current-level determination means and the time-limit selector.
According to yet a further aspect, the present invention which achieves these objectives relates to a power-generation-system installing method including the step of connecting a power generation system including a DC power supply, including at least a transformerless inverter and an earth floating capacitance, to a low-voltage distribution system to which a plurality of consumers, each having an earth leakage breaker, are connected and one wire of which is grounded, via a receiving-end earth leakage breaker. An operation time of the receiving-end earth leakage breaker is set to a value larger than an operational time limit of the earth leakage breakers provided in the consumers.
According to still another aspect, the present invention which achieves these objectives relates to a power-generation-system installing method including the step of connecting a power generation system including a DC power supply, including at least a transformerless inverter and an earth floating capacitance, to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker. In the method, ground-direction determination means for determining whether a ground position is inside or outside the power generation system is provided.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.